When describing specific, defined plural nouns (like "the new apps" or "these funny websites"), you must use the weak plural form of the adjective.
The Universal -u Ending
The weak declension in the plural is straightforward: for all three genders and across all four cases, the adjective always ends in -u.
Notice how the adjective ends in -u, regardless of the noun's gender or whether it is in the nominative or accusative case:
| Do you always use the new apps? | Notar þú alltaf nýju öppin? |
| Where are the popular podcasts? | Hvar eru vinsælu hlaðvörpin? |
| We need to click on the bad links. | Við þurfum að smella á slæmu tenglana. |
Dative Plural
Even when the noun changes—like in the dative plural, where definite nouns end in -unum—the weak adjective remains -u. For example, the verb deila (to share) requires a dative object:
| I share the funny websites on the internet. | Ég deili fyndnu vefsíðunum á netinu. |
| You need to share the popular apps. | Þú þarft að deila vinsælu öppunum. |
U-mutation in Plural Adjectives
Because the weak plural ending is -u, it triggers U-mutation if the adjective has an a in its stem, changing that a to an ö. For example, gamall (old) becomes gömlu:
| He shares the old links. | Hann deilir gömlu tenglunum. |